Signaling system



Y- 19.49 H. M. BASCOM ETAL 3 SIGNALING SYSTEM Original Filed Aug. 17, 1944 2 Sheets-Sheet 1 OSCIL 1.4 T0)? FIG TRANSMI TTER COUNTING CHAIN KS R30 R m s am; INVENTORS B 0's TEND ORF, JR.

A7" TOPNE Y Nov 15, 1949 H. M. BASCOM ETAL SIGNALING SYSTEM 2 Sheets-Sheet 2 v Original Filed Aug. 17, 1944 WWCU Btu A 23.6

TENDORF; JR.

HJJ. BASCOM INVENTORS MASSONNEAU ATTORNEY Patented Nov. 15, 1949 srcmnmo srsrnm Henry M. Bascom, New York, Robert F.

neau, Scarsdale, Bernard Ostendort, Jr.,

ma'ica, and Wilton T. Rea, Manhascet, N. Y

Marcon- Jaassignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a

York

549,842, now Patent No. 30, 1948. Divided and 25, 1947, Serial No. 744,008

This invention relates to signaling systems and more particularly to a system of the type disclosed in our copending application Serial No.

549,842, filed August 1'7, 19%, now U. S. Patent 2,438,492 of March 30 1948, of which the present I application is a division and in which a predetermined number of half cycles of an alternating current transmitted from a'distant point are received in a circuit which responds to both positive and negative halt cycles of the transmitted wave, inverts the negative half cycles and causes both the positive half cycles and the inverted negative half cycles to be recorded by the tubes of a counting chain, said tubes conditioning, in succession, the tubes of a second chain for operating the tubetherein last conditioned subsequent to the reception of the last half cycle of the signal train.

The variousfeatures of the invention will be understood from the following description when considered in connection with the accompanying two sheets of drawings, the scope of the invention being more particularly pointed out in the appended claims.

In the accompanying drawings, Fig. 1 shows the transmitter and Fig. 2 shows the receiver, said 4 Claims. (Cl. 177-35?) corporation of New Original application August 1-1, 1944, Serial No.

2,438,492, dated March this application April ble triode tube RL; a detector, inverter and impulse amplifier operating on odd half cycles, all of which comprise three of the triodes oi the doll-- ble trlode tubes DETl, DET2 and INV; a detector and impulse amplifier operating on even half cycles which comprises two triodes of the triode tubes DETZ and INV; a recycling circuit comprising the two triodes of vacuum tube RE and the vacuum tubes EXT and SEL; a counting chain circuit consisting of ten cold cathode gasfilled tubes CTR! C'I'Ril; and a marking chain figures being placed adjacent, to each other from left to right in the order named to disclose the invention completely,

The transmitter, shown in Fig. 1, comprises a start-stop oscillator of the type disclosed in Patent No. 2,370,685, issued to W. T. Rea and J. R. Wilkerson on March 6, 1945, a counting chainconsist ng of ten cold cathode gas-filled tubes CTI GTO, a recycling circuit comprising two cold cathode gas-filled tubes GI and G2 by means of which single or repetitive transmission of a pulse train is accomplished, a line coupling circuit comprising a potentiometer network R23 R29 and a line amplifying tube L by means of which the oscillator is coupled to the line, the double triode D by means of which it is insured that only the predeterminednumber of oscillations are caused to be applied to the line,

an impulse control circuit including the transformer IT and the uppertriode of tube A by means of which each half cycle applied to the line is caused to be registered on one of the tubes consisting of the ten cold cathode gas-filled tubes Si S0.

Referring now more particularly to Fig. 1, the general operation of the transmitter is as follows:

During the interval. when no signal is being transmitted the oscillator 0C is held in a nonoscill'ating condition and the line coupling circuit is so conditioned as to prevent any impulses from being applied to the line. At this time, all the tubes CTl CTO of the counting chain are maintained in the non-conducting condition. Now when a signal consisting of a certain number of positive and negative half cycles of a continuous alternating current train is to be transmitted over line LN, a connection is made between a, common conductor and a tube in the counting chain CTl GTO that marks the last of the counting chain CTI C11), and a restoring circuit including the upper triode of tube B and the vacuum tube (3' which, under the control of the aforementioned recycling circuit, extinguishes the tube of the counting chain.

The receiver, shown in Fig. 2, comprises a twostage direct current amplifier employing a douhalf cycle of the desired signal train. At this time the recycling tube G2 becomes energized to condition the tubes of the counting chain for operation, starts the oscillator. 06 and removes the block in the line coupling circuit. The sine wave produced by the oscillator 00 is thus permitted to-be impressed on-the line LN. Each time the oscillator completes a half cycle it causes an impulse generating circuit to produce an impulse which fires one of the tubes of the counting chain, and each tube, as it fires, conditions the succeeding tube to be fired by the following impulse. Thus the tubes of the counting chain are fired in succession by the successive half cycles of the signal wave until the tube associated with the chosen selecting lead is fired. The firing of this odd number of half cycles have been produced, I I

the oscillator will continue operating to produce the succeeding even half cycle since the current in the elements of the oscillator is then flowing in the non-conductive direction of the oscillator stop" tube. This half cycle, however, is pre-- vented from being applied to the line by the line I clamp tube D.

After a short delay, one of the tubes oithe recycling circuit fires, causing the tubes of the counting chain to be extinguished but still maintaining the oscillator stopped and the line coupling tube in the non-transmitting condition. The circuit is thus returned to its initial condition, ready for the transmission 01' the next signal wave.

In the present embodiment of the invention, the transmitter has been arranged to send a desired digit either singly or continuously. For the latter type of operation, the recycling circuit is arranged so that, as long as a connection is maintained between the common lead and a selecting lead, the signal corresponding to the selection will be represented with a recycling pause between groups or half cycles of about men milliseconds. In the receiver, during an interval when no signal is being received, all tubes of the counting chain C'I'Rl CTRO are maintained'in the non-conducting condition. When a signal is received, the first half cycle, which is positive, causes an essentially square negative wave, produced in the anode circuit of the first detector, to produce a positive square wave in the anode circuit of the inverter associated with this deteeter. This charges a condenser associated with the recycling circuit, the latter then acting to apply energizing potential to anodes of the tubes in the counting chain. Near the end of the first halt cycle or the signal train, the first detector cuts ofi, causing the associated inventer and impulse amplifier to apply a positive voltage impulse to the odd tubes of the counting chain. The first tube of this chain being the only one normally primed, fires, priming the first marking tube and-the second counting tube. Near the end of the second half cycle, the second detector cuts oil, applying a positive square wave to the recycling circuit. The condenser of this circuit is arranged so as to discharge with comparative slowness and hence to prevent the recycling function from occurring during the interval between the termination of the positive square wave produced by the first detector's inverter and the beginning of the one produced. by the second detector. Near the end of the second half cycle, current flow is initiated in the anode'circuit of the second detector, causing the associated impulse amplifier to apply a positive voltage impulse to the even number counting tubes. Since the second tube oi. this chain is now primed by the conducting condition of the first tube, it fires, priming the third counting tube and the second marking tube and removing the priming condition from the first marking tube. In a like manner the counting .tubes fire in turn, each priming the corresponding marking tube and the following counting I tube and removing the priming condition from the preceding marking tube.

When the last half cycle or the signal train .is received, the positive square waves are no longer applied to the recycling circuit by the first detectors inverter and the second detector. The recycling circuit condenser discharges, causing the recycling circuit to apply a positive impulse to all marking tubes and immediately thereafter to extinguish ali'counting tubes. Since at this time the only primed marking tube is that corresponding to the last fired counting tube, it is fired by the'impulse and acts to extinguish any other marking tube that may previousl have been fired. The desired selection is thereby recorded and the counting chain is restored to its initial condition ready for the reception 01' the succeeding signal.

The detailed, description of the circuit now follows: a

To prepare the transmitter for signal transmission, key K is depressed and the filament circuits (not shown) for all the vacuum tubes are activated. A breakdown potential difierence for the main gap 0! recycling tube GI is thereby applied lbetween the anode 'and cathode thereof, positive potential Irom positive battery +V being applied through the contacts of key K and resistor Rl to the anode of tube GI, and negative potential being applied to the cathode 01 said tube through the voltage divider composed of grounded resistor RI! and serial resistors R1 and R8 connected, in parallel with resistor Rll, to battery V. The difierence of potential thus applied between the cathode and anode of tube GI is suificient to cause the ionization of its main gap and the same is thereby rendered conducting to draw current therethrough over the abovetracedcircuit. whereupon certain specific potentials are made available at the terminals of various electrodes, terminals and conductors connected with the circuit as indicated below:

The current flowing through the cathode-anode circuit of tube GI causes a potential to be available at the left terminal of resistor R6 which is applied by direct connection to the grid or the upper triode of vacuum tube B. The ohmic value of resistor R6 is So cOmDuted that the potential applied to this grid will be such that the resulting current flowing through the anode-cathod circuit of the upper triode of tube B will produce a potential on the grid of the extinguisher tube 0 which is so negative as to cause said tube to be virtually non-conducting but not wholly so as later explained. The circuit through the upper triode of vacuum tube B may be traced from negative battery V, resistor RIO, and a resistor R89 shunted to ground, cathode-anode oi the tube to positive battery +V through resistor R8 and, in parallel therewith, resistor R1! to ground; The potential available at the Junction point of resistors R15, R8 and R9 consequent to this flow of current is sufiiciently less positive than the full potential or the battery +V as to be a little above the cut-oil point or the tube C. Since the cathode of the tube C is connected to all of the anodes 0f the gas-filled tubes CTI GTO and since the cathodes of the latter have a negative potential applied thereto from negative battery V through an'undesignated resistance individual to each 01' the cathodes, the trickle of aninfinitesimal current flowing over the path from positive battery l-V, anode-cathode of tube 0, anode-cathode 01' each of the tubes CTI CTII, to negative battery V via the undesignated each 01' the cathodes of resistance in series with the tubes CTI CTO, causes a positive potential to be available at the cathode of tube C which is applied to the anodes of each of the tubes CTI CTII, which potential, however, is less than required to sustain conductivity. However, since at this time all these tubes are inactive even though a microampere or two is flowing through them as above set forth, the application 01' less sustaining positive potential to the anode! ,thereof by the cathode of tube C-will have no eilect.

The current through the anode-cathode circuit of tube GI is also'eii'ective in producing another less negative potential which appears at the right terminal of resistor'RO and is applied, through resistor R2l to the grid of the lower triode of tube 3. Since negative battery through resistor R22, with resistor R90 shunted to ground is con-; nected to the cathode of this lower triode, and the anode thereof is connected to the upper terminal of the oscillator coil DC (the lower plate of condenser OCN and the lower terminal of the, coil both being connected to ground), cur--- tions no oscillations will be produced for transmission over the line LN.

It will be observed that the upper grid of the as one time of tube p m as a low mam circuit between the network and ground for currents generated in the direction of its conductivity and the other triode is a low resistance circuit between the network and ground for currents generated in the direction of its own conductivity, thus preventing tube L from transmitting signals over'the line. In other words, as

long as key K alone is operated and none of the numerical keys i li ot-,key set K8 is operated, the condition of the transmitter is such that the oscillator coil 00 is blocked,less than sustaining potential is applied to the anodes of the tubes CTI CTDJJ! the counting chain and a high attenuation is established across the line LN by the triodes of tube D to prevent curv rents in either direction from getting through.

line clamp" vacuum tube D is connected to the common terminal of resistors RM, RM and RH and that the lower grid is connected to the common terminal of resistors RI i, RM and Bit. Resistors RH and Rl5 are connected to positive battery +V via the contacts of key K; resistors RH and RH are connected, over conductor i, to the lower moving contact of each of the numcrical keys i 0 of the key set KS and to a voltage divider comprising resistors R20 and R5 bridged between battery --V to ground; While resistors RH and Ri 2 are connected to the cathode of tube GI. Now resistors Ril, R12, RM, Rib, Rll, RM and resistors R20 and R5 (the latter two resistors comprising a voltage divider) are computed to such values that when tube GI is rendered conducting, the grids of both triodes of tube D are rendered relatively positive, and if signal voltages be applied current will flow through both triodes effectively to short-circuit the line LN as subsequently set forth.

It will further be noted that the line LN over which the signals are to be transmitted is connected to the cathode of the line amplifier tube L and, also, to the left terminalof the low resistance resistor R23 which has its right terminal connected to ground. Resistors R24 R28 form a network-which interconnects the grid of the line amplifier tube L and the mid-terminal of oscillating coil 0C, and the object of this network is to couple the oscillator coil 0C with, the line LN and with means to stop instantly the transmission of signals over the line LN through the control exercised by both triodes of tube D. It will also be observed that the anode of the upper triode of tube D is connected to ground and that the cathode is connected to the aforementioned resistance network at the junction of resistors R26 and R21, whereas the anode of the lower triode is connected to the network at the Junction of resistors R25 and R26 while the cathode is connected to ground. Since each triode of the vacuum tube D conducts in one direction only, since both triodes are oppositely connected and since, as before described, the grids thereof are kept at a relatively positive The present embodiment of the invention is arranged either for the repetitive transmission oi the same digit or for theJsingle transmission of one digit only, the digit transmitted in either case being-controlled by whichever numerical key of the key set KS is depressed, key B2, in its operated position, controlling the transmission of a single train of impulses and in its normal position controlling the repetitive transmission of the same train of pulses indicated by the operated numerical key. Assume, therefore, that a single signal train of pulses corresponding to a "5 selection is to be transmitted. -With key S2 operated, the numerical key 5 ofhey set Kid is then operated. With key S2 operated, resistor R35 which is, connected to the anode oi the tube G2 and to the left plate of condenser C3 is grounded, and since current for the circuit or? tube G2 is drawn from battery +V through resistor R2, the grounding of resistor R35 causes it to be connected in shunt with resistor R2 so that the potential available at the anode of tube G2 for applying a charge to the left plate or condenser 03 is less than that available through the anode of tube G! for charging the right plate of said condenser. The operation of key 5 connects, through its lower contacts, the cathode of counting tube GT5 to conductor i, while through its upper contacts it completes a charsing circuit for condenser cl 01' large capacity and condenser Ci of relatively smaller capacity, the charging circuit of condenser C2 extending from positive battery +V, contacts of irey K,

resistor R30, upper contacts of key 5, condenser C2 to ground. The charging circuit for con" denser Ci extends from battery +V through contacts of key K, resistor R", upper contacts of key 5, left operated contacts of key S2, condenser Ci, resistor RSI to the potentiometer arm of resistor R32 (which is one of the resistance elements of the potentiometer network extending from battery V to ground via resistors RI, RM, R33, right-hand inner operated contacts of key :52 to ground). The impulse thus created in the condenser Ci raises the potential of the control anode of G2 tube suiilciently to cause ionization of the critical gap thereof, inasmuch as the oathode is connected to the negative battery --V. This ionization spreads to the main gap since positive battery from source +V is applied to the anode of the tube via resistor R2 and the contacts of key K. The impulse applied to the control anode of tube G2 is delayed by the time required to-charge condenser C2 since this condenser being of larger capacity than that of condenser Ci delays the full charging of the latter. This arrangement prevents the transmitter from potential when tube Gl is conducting, it follows 16 being started prematurely in case the upper con- 7 tacts of key close before its lower contacts. This, of course, could be obviated by a sequence adjustment of the key contacts.

There is, moreover, a relatively large capacity C3 connected between the anode of tube GI and that of tube G2. During the conductivity of tube GI, the right plate of this condenser acquires a charge, of course, which depends upon the potential available at the anode of the tube GI. When tube G2 fires, a parallel path to resistor R35 is established through tube G2 thus lowering the potential at the anode of tube G2. The lowering of the potential on the left-hand plate of condenser C3 (connected to the anode of tube G2) causes condenser C3 to begin to charge and since the charging current is drawn through resistor RI, the anode of tube GI is momentarily made much less positive and the latter tube is extinguished. A negative source of voltage is furnished to the cathode of tube GI via its connection to the Junction of resistors R6, RIG and RI3, which resistors form part of a potentiometer circuit extending from negative battery V, via the combination of resistors RI6 in parallel with serially-connected resistors R1 and R6, and thence via resistor RI3 to ground. The extinguishing of tube GI causes the flow of plate current in this potentiometer circuit to cease, and the potential of the cathode, and of lead 2 connected thereto to become more negative. The grids of both triodes of tube D, by virtue of their connection to lead 2 via resistors RH and RI2, assume a negative polarity, said grids now eiTectively preventing any current from flowing through their associated anode-cathode circuits so that any energy which is thereafter produced by the oscillator is applied to the amplifying tube L instead of being short-circuited to ground through the triodes of tube D. The signal ap-- plied to the grid of tube L will thereafter partly be carried to ground over resistor R23 and partly applied over the line conductor LN to the receiver.

The extinguishing of tube GI further causes the potential at the junction of resistors R1 and R6 to become more negative, and this potential is applied to the grid of the upper triode of tube B. In a similar manner the extinguishing of the tube GI causes the potential at the junction of resistors R2I and R34 to become more negative and this potential is applied to the grid of the lower triode of tube B. The lower triode of tube B, it will be remembered, operates to supply the oscillator coil 00 with direct current during the times that the grid of said lower triode is positive; that is, during the time when tube GI is conducting. Hence, when tube GI is extinguishedand the lower grid of tube B is made negative as an indirect result of the conductivity of tube G2, this current is suppressed and the energy stored in the oscillator coil 00 and condenser OCN begins to oscillate to produce a continuous train of alternating current waves as set forth in the-above-mentioned patent, the lower triode of tube A functioning to supply the required energy to produce sustained oscillations. Since the anode of the lower triode of tube B is connected to the common terminal of oscillator coil 00 and condenser OCN, the first half cycle of the current will be positive.

It will be remembered that during the conductivity of tube GI the current flowing in the oathode-anode circuit thereof caused the grid of the upper triode of tube B to be maintained at a positive potential so that this triode would conduct 8 and that, in consequence, a relatively negative potential was applied to the grid of tube C which established an inappreciable current through the anode-cathode circuit thereof, including the cathode-anode path of each gas-filled tube in the counting chain CTI CTI). Now when tube GI is extinguished, cessation of the anode-cath ode current through the upper triode of tube B causes the anode to become more positive in consequence of which the grid of tube C is made more positive. The greater current now flowing through anode-cathode ciruit of tube C raises the available potential at the anode of each of the counting tubes CTI CTI! to a value such that, when one of them is rendered conducting through its control gap as hereinafter set forth, the voltage available at the anode of that tube from the cathode of tube C will cause said tube in the counting chain to become conducting through its main gap, thus causing it to remain operated when the initial breakdown voltage between its cathode and control anode is removed.

The output of the oscillator is picked off the mid-terminal of the oscillator coil OC and applied to the resistor R28 whence, through resistor R29, part of it is drained off to ground and whence, through a voltage divider composed of resistors R21, R26, R25 and a portion of the resistor R24, a part of it is applied to the grid of the line amplifying tube L, whereby the anodecathode current in this tube is caused to be modulated in accordance with the character of the oscillating voltage applied to the grid thereof which, in turn, is proportional to, and in accordance with, the character of the voltage produced by the oscillator coil 0C. The anode-cathode oscillating current in the line tube L passes through resistor R23 which is connected between the cathode of the tube and ground, and the voltage drop developed across this resistor is applied to the line conductor LN for transmission thereover to the receiver which, as set forth hereinafter, responds to the oscillations and provides a suitable indication thereof. It should be noted at this point that if the grids of both triodes of tube D were not rendered negative when tube GI is extinguished, the oscillating energy, instead of being applied to the line LN as above noted, will pass to ground, the positive half cycles of the energy passing through one triode of tube D and the negative half cycles passing through the other triode of tube D. The fact that the grids of this tube are rendered negative at the time tube GI is extinguished causes the triodes of this tube to present practically an open circuit to the potentiometer network between the oscillator and the grid of the line amplifier tube L so that the oscillations are reproduced in tube L and passed into the line conductor LN.

The upper triode of tube A together with transformer IT form an impulse producing device. The grid of this triode is connected serially through the high resistance resistor R15 to the common terminal of the oscillating coil 00 and condenser CON, and the alternating voltages produced by the oscillator correspondingly alter the potential of said grid. These voltages, however, are so large that they drive the grid from the point of cut-off to a positive value, a fact which, coupled with the additional fact of the high resistance of resistor R16 causes an anodecathcde current flowing through the upper triode of tube A to be essentially a square-top wave. Now the first half cycle produced b the oscillator is positive and during this period our-- 7 rent will flow in the upper triode of tube A the anode-cathode path, to ground on the cathode. At the end of the first half cycle, the grid of the upper triode of tube D becomes negative with respect to its cathode, and anode current, therefore, ceases to flow through the primary of transformer IT. The cessation of current is very abrupt due to the square-top character of the wave, and a sharp impulse is thereby caused to be generated in the secondary winding of transformer IT, which appears as a positive impulse at terminal 2 connecting with the control anodes of the odd numbered tubes CTI T8, and as a negative impulse at terminal I, which is connected to the control anodes or the even numbered tubes GT2 CTII. The control anode of tube CTI, however, is at ground potential.

Since the cathodes of all the counting tubes CTI CTII are connected to negative battery V through appropriate resistances, the application of the positive impulse to the control anode of tube CTI via its associated undesignated condenser raises the potential of said control anode to a value which establishes a control gap breakdown diflerence of potential between it and the negative potential available at the cathode, causing the control .gap to ionize. Since an appropriate positive potential is, at this time, also applied to the anodes of all counting tubes from the cathode of tube C, as previously explained, ionization of tube CTI spreads to the main gap, in consequence of which the tube will remain in a conducting state upon the termination or the impulse, the current flow path through the main gap of tube CTI tracing from positive battery +V through the anode-cathode path of tube C, anode-cathode path through the tube CTI, and the undesignated cathode resistance to negative battery V. The flow of current through the cathode resistor of tube CTI produces a relatively positive potential at the cathode which is applied to the control anode of the next tube 0T2,

through an interconnecting resistor. This potential, however, is not sufllcient to cause the breakdown of the control gap of tube 0T2, said potential serving only to bias the control anode of this tube for breakdown purposes upon the application thereto of an additional potential over that which supplies the bias. The other odd numbered tubes to whose control anodes the positive impulse from transformer IT is applied at the time it is applied to the control anode of tube CTI are not fired with tube CTI because, while the control anode of tube CTI is normally at ground potential, the control anodes of the other odd numbered tubes are maintained at a voltage more negative than ground by means of the resistance network interconnecting -V and ground.

At the end of the second half cycle, current flow is again initiated in the plate circuit of the upper triode of tube A, the change in current being effective to produce an impulse in the primary windings of transformer IT which is opposite in polarity to that-produced at the end of the first half cycle and, consequently, causing a positive impulse to appear at the No. 1 terminal of the secondary'windings of transformer IT and a negative impulse at the No. 2 terminal. Since the control anode of tube GT2 is already relatively positively biased by the cathode poten- 10 the positive impulse now applied to the control anode of tube 0T2 will cause it to flre, in turn conditioning the control anode of tube CT! to be responsive to the next positive impulse to be applied thereto from the No. 2 terminal of transformer IT. A series combination of varistor VR and resistor R38 shunted across the two primary windings oi transformer 1'! serves to equalize the amplitude of the impulses produced at the ends of the odd and even half cycles, which amplitudes would otherwise be unequal because the in ductance of the primary winding causes its current to rise more gradually at the ends or even half cycles than it decays at the ends oi odd bald cycles.

' In the above manner, counting tubes CTI 0T5 fire, each in turn conditioning the succeed ing tube. When, at the end of two and a hair cycles, tube 0T5 fires, the flow, oi current between its anode and cathode renders said oathode relatively positive. Since the cathode of this tube is connected to conductor I through the lower contacts of the numerical key 5, and the conductor is, in turn, connected to the grid of the lower triode of tube B via resistor R34 and to the grids of both triodes of tube D via resistors RI! and RIiI, all of said grids are rendered positive.

As a result the anode-cathode impedance of both triodes of tube D is reduced to a fairly low value, the signal from the oscillator is greatly attenuated across the potentiometer resistor R24, and the tube L is prevented, after the transmission of two and one-half cycles, from applying any further signal energy whatsoever to the line conductor LN.

Due to the fact that, at the end of the two and one-halt cycles, current in the oscillator 00 is flowing toward ground and since the upper termi-- nal or the oscillator is connected to the lower anode of tube B, the triode of which this anode is a part will fail to conduct even though its grid is positive with respect to its cathode. The oscillator 00, therefore, rails to stop until, at some time later near the end of the third cycle. the current reverses, the anode oi the lower triode of tube B becomes more positive than the oathode and current again flows through this triode to thereby return the oscillator to its steady state stopped condition as originally described.- This. however, will in no way affect the line since, as before stated, the conductivity of the two triodes of tube D prevents such voltage from being impressed on the grid of tube L even though the oscillator 0C is still functioning.

The positive potential upon conductor I is also applied to the control anode of tube GI through resistor R31. After a delay due to the time required to charge condenser 04, tube GI fires across its control gap and thence-across its main gap to cause its anode potential to become more negative and its cathode potential to become more positive. Due to the connection of condenser C3 between the anode of tube GI and that of tube G2, and due to the fact that this condenser is charged to the voltage of the drop across resistor R2, the fact that the anode of tube GI is rendered more negative causes an impulse to be generated which is transmitted across the condenser C3 to render the anode of tube G2 also more negative. In consequence, tube G2 is extinguished. Further, due to the conductivity of tube GI, the left terminal of resistor R6 is made more positive than it was before, and this positive potential is, of course, applied to the grid of the upper tial derived from the conductivity of tube CTI, triode of tube B to cause current to flow through ll its'anode-cathode circuit. The anode being renof the counting tubes is insufiicient to maintain a discharge. Tubes CTI to CT! therefore become extinguished.

The extinguishment of tube CTI causes conductor I to become more negative, but the eil'ect of this on the grids of tube l3 and that of the lower trlode of tube B is compensated for by the fact that the cathode of tube GI has become positive by an equal amount. The reason for this is because the more positive potential at the oathode of tube GI is applied to the lower grid of tube 8 via resistor R2I at the same time that conductor I supplies a less positive voltage to the same grid via resistor R34. In the same manner, the more positive potential on the cathode of tube GI is applied to the two grids of tube D via resistors RI 2 and RH at that same time that conductor I supplies a less positive voltage to these grids via resistors RH and RIO. Since,

the firing of tube .GI and the extinguishing of tube CTI occur practically simultaneously, the grids of the above trlodes remain at a substantially constant potential. The circuit is thus returned to its initial condition except for the fact that, since numerical key 5 is closed, condensers CI and C2 remain charged overpreviously described paths and, therefore, no impulse will be produced across condenser CI to fire tube G2. To produce the impulse, numerical key 5 is released and key 5 or some other numerical key reoperated. Upon release, condensers C2 and CI are discharged and, upon reoperation, condenser C2 will be charged and later condenser CI will be charged as previously described, producing an impulse that will cause tube G2 to fire and the operations above described to be repeated.

Other signals may be sent in the same manneras-above described except that in the case of even numbered signals the oscillator stops immediately at the end of the last half cycle of the signal since the direction of current flow at this time is in the conductive direction of the lower trlode of tube B and the voltage applied to the platen! this trlode is more positive .than that of the cathode.

For the continuous transmission of the same signal only the numerical key corresponding to the number of the signal to be transmitted is operated, key S2 being kept in its unoperated condition. At the end of each signal train when tube GI has fired and extinguished tube G2, the latter tube refires across its control gap after a delay which maybe controlled by the adjustment of the potentiometer R32. The reason for this is that when tube GI extlnguishes tube G2, the anode potential of the latter becomes more positive with respect to the potential supplied by battery -V at the cathode. However. due to the fact that key 82 is normal, the control anode is tied to the main anode via resistors R3 I, R32 and R33. Hence the potential of the control anode similarly becomes more positive with respect to the potential available at the cathode. Both these potentials, however, are derived, from the charging circuit of condenser C3 which includes battery V, resistors-R3, R32, and R33, right inner normal contacts of key S2, condenser 03, resistor RI, contact of key K to positive battery detector tube DET2 battery as above +v: In parallel therewith there is also the poem-- tial'available at the lower terminal of resistor RI due to theconductivity 0! tube GI, and also the parallel resistor R2 to battery +V through the contacts 01 key K. The potential applied to the control anode of tube GI, being derived from the above network and ably adjusting the potentiometer R32. When the appropriate value of potential is reached, tube G2 will fire across its control gap and the operations above described will be repeated. Thus, without ing. In the transmission of a "1" signal, for

example, the, duration of the signal may be 2 milliseconds. If tube GI were to be tired immediately by the positive potential on conductor I, it could remain extinguished for only 2 milliseconds whereas the deionization of a tube of this type requires at least 5 milliseconds and the value of condenser C3 is such as to delay the rise 0! plate potential sufilciently to permit such time for delonization. delay in the firing of tube GI (which can be arranged by the proper choice of values for condenser Cl and resistor R31), it can remain extinguislhed for 6 milliseconds in the transmission of a l ,1

that during continuous transmission of this shortest signal combination, and with a recycling scribed. It is assumed that filament current for' the vacuum tubes of the receiver flows through the filaments thereof from any suitable source of current (not shown) and that, in consequence, the respective cathodes of the tubes are in an emitting condition. In the no-signal condition, no current flows through the upper trlode of detector tube DETI since the grid thereof is maintained at a cut-off negative potential which is derived from a voltage divider comprising resistors R40 connected to negative battery V through conductor 5, RBI and R, the latter being connected to a positive source of potential +V over conductor 2. The ohmic values of resistors RBI and R40 are computed to a value that 'will permit no current flow through the anode,- cathode circuit of the upper trlode of tube DETI. On' the other hand, current is flowing through the anode-cathode circuit of the upper trlode of because the potential at the grid thereof is available from the voltage divider comprising resistors RH connected to negative battery V over conductor 5, and resistors R and R, the latter being connected to positive mentioned. The ohmic value of resistors R and R is computed to a value that will permit current flow through the anodecathode circuit of the upper trlode of tube DET2, the path of said circuit tracing from positive battery +V to conductor 2, conductor 4, resistor R42, through the anode-cathode path within the upper section of tube DET2, to cathode ground.

INV is connected to the ode of tube DETI anode of the upper tribeing a function of time, can derived for any particular time value by suitand the correspondingly recycling time in continous send- However, with a 4-millisecond signal, Thus the circuit is so arranged through the voltage divider connected to negative battery -V, and the resistors of this voltage divider are computed so that the normal potential on said grid permits current to flow through the upper anode-cathode of said tube INV, the path of said ci cuit tracing from positive battery +V, conductor 2, resistor R64, through the upper anode-cathode path of the tube INV to cathode ground. Thus current flows in the anode-cathode circuits of the upper triodes'oi tube DET2 and the inverter tube HIV and the potentials on the anodes oi the upper ,triodes of both tubes are applied through resistors R41 and R50. respectively, to the plate and grid of the lower triode of tube RE. Resistor R48 is connected to and through RSI to condenser A and to battery V over conductor 5 so that, with the positive potentials on the anodes of the upper triodes of tubes DETZ and INV obtaining at this time, the potential at the Junction point is negative with respect to ground and causes condenser A to be charged negatively throughresistor RSI. The negative potential on condenser A is applied to the grid 01 the upper triode of the recycling tube RE via resistor R52, thereby causing no current to fiow through the anode-cathode circuit thereof. Since the grid of the lower triode of the inverter tube INV is connected to the upper anode of tube RE through resistor R82, the potential on this grid, as modified by the connection of said grid to negative battery V via resistor R8! is, therefore, positive with respect to its cathode. This permits current to flow through the anode-cathode oi' the lower triodeof tube INV, and the potential on the anode of this triode, which is relatively negative due to the fiow or plate current from positive battery through resistor R19 is transmitted to the grid of the extinguishing tube EXT through, resistors R54 and R53. The value of this potential causes only a very slight current flow through the anode-cathode of tube EXT and the anode-cathodes of each of the gasv filled tubes of the counting chain CTRI BL is maintained at a, slightly negative potential through resistor R58, variable resistor R59 and resistor R80 which is connected to negative battery -V. Under this condition, some current fiows through the upper triode path which extends'from positive battery +V, resistor R51, anode-cathode path to cathode resistance ground. The anode of the upper triode of tube RL is. therefore, at a potential less positive than the full positive battery potential, and this potential,

as modified by potentiometer comprising resistors R55 and R56 to negative battery -V, is connected to the grid of the lower triode of this tube, thereby maintaining said grid at a, potential which will cause some current to flow through the anode-cathode circuit thereof, said circuit extending from positive battery +V, resistance R45, anode-cathode path to cathode resistance ground. In eflect, this arrangement makes the tube RL a two-stage direct current amplifier since a change of potential on the grid of the upper triode will cause an amplified voltage change on the anode which, through resistor RIB, is applied to the grid of the lower triode,

causing a further amplified change in voltage to appear in the anode of said lower triode.

The first half cycle oi. the incoming. signal, which is positive, is applied to the grid of the upper triode of tube RL, causing the potential thereof to be rendered less negative. More current now flows through the anode-cathode circuit of the upper triode of this tube, and the potential developed across resistor R55 as a result or the increase in current renders the grid of the lower triode more negative than previously, and thereby increases the potential of the lower anode. For small values of signal voltage this increase in potential is a two-stage amplification of .the potential of the first half cycle of the incoming signal. For larger values oi signal voltage the peak of the half cycle may be flattened as the grid of the lower triode attains a'potential which causes the cessation of current in the anode-cathode path,

but this will not adversely ailect the action of the receiver.

The potentials across the voltage divider comprising resistors RBI and R40 and across the voltage divider comprising resistors R44 and R4! which result from the amplification or the signal are applied, respectively, to the upper grids of detector tubes DETI and DET2. Since the first received signal is positive, these grids become more positive and, at some value of signal which exceeds the noise level on the line circuit LN, current fiows through the anode-cathode circuit of the upper triode of detector tube DETI. The current fiow in said triode causes the potential or its anode to become more negative, and this more negative potential is applied, via resistor R46, to the grid of the upper triode of inverter tube INV. The anode potential of this triode now, becomes more positive, but this has little eflect' on the grid of the lower triode of tube DETI to which it is connected by way of condenser B since its grid is already positive with respect to its cathode due to the potential available on said grid as a consequence of its connection to the common terminal of resistors R63 and R62. Since little or no current is flowing through the upper triode of tube INV, the anode thereof is relatively positive by virtue of the small voltage drop in resistor R64 which interconnects said anode and positive battery +V on conductor 2. Hence, while this anode is relatively positive during the time that no current flows through the associated anode-cathode circuit, this positive potential is also available at the anode of the lower triode of the recycling tube RE, which is used as a diode, so that current flows through the anode-cathode circuit and a positive charge is applied to condenser. A. Since the plate or this condenser is connected to the grid of the upper triode of the recycling tube RE via resistor R52, said upper grid likewise acquires a positive potential the effect of which is to cause the associated upper anode of this tube to become more negative, carrying with it the grid of thelower triode of tube INV. This causes the potential at the anode of the latter triode o1 tube INV tobecome more positive, carrying the grid of tube EXT towards positive also. Thus, the cathode of tube EXT is permitted to become sufilciently positive to apply to the anodes of the counting tubes CTRI CTRO an anode-to-cathode potential greater than their sustaining potentials.

The change toward positive of the anode of the lower triode of tube INV applies a positive impulse through condenser D to the grid of triode BEL. Since said grid already has a positive poassays:

Bill, the anode-cathode current is little efi'ected and hence the anode potentiaLremains substantially constant. It should be remembered that during the reception of the first hall cycle or signal, positive potential was not only applied to the grid of the upper triode of tube DETI as already explained,'but also to the grid of the upper triode of tube DETI. Since this merely constituted an increase of the existing positive potential applied through resistor R42 to said grid, and in consequence of the large value of resistor R42, only a small increase in grid current results, and there is practically no change in the anode-cathode current in the upper triode of tube DET2. The anode potential therefore remains substantially constant.

Near the end of the first half cycle oi the sinusoidal wave produced b the transmitter, the

grid of the upper triode of tube DETI becomes negative with respect to the cathode, the signal being applied to the grid of this upper triode through the two-stage amplifier comprising both triodes oi tube RL. The anode potential of the anode of the upper triode oi tube DETl, therefore, increases in a positive direction which, in turn, causes the grid or the upper triode of tube INV also to become more positive. The increased current now fiowing in this last-mentioned triode causes the potential on its anode to become more negative. The resulting negative impulse, applied through condenser B, to the grid of the lower triode of tube DETI causes a positive impulse, produced on the anode of this triode, to be applied through condensers ON I, CN3, CNS, CN! and CNS to the control anodes of the odd-numbered tubes CTRI, CTR3, C'IRi, CTR! and CTR9 of the counting chain. Unaided, the magnitude 01' this impulse is insuflicient to fire the control gaps or these tubes, but since the control anode of tube CTRI is provided with a positive bias relative to its cathode through resistors R65, R61 connected to ground and resistor R86 in parallel thereto connected to negative battery V, tube CTRI fires across its control gap to the nega-' tive potential at the cathode supplied from battery V through an undesignated resistor. The tube then fires across its main gap to the positive potential supplied by the cathode of tube EXT and remains in a conductive state until this potential is removed or reversed.

When tube CTRl fires, the current drawn through its anode-cathode circuit causes the cathode potential to become more positive, carry-- ing with it, in the positive direction, the control anodes of tubes CTR2 and Si, the latter tube being the first tube in the marking chain. The potential for the control anode of tube CTR: is applied through resistor R69 while that for the control anode of tube Si is applied through resistor R10. The applied potentials are, however, insufiicient to fire either of these two tubes because, in the case of tube CTR2, the diflerence in potential between the control anode and the cathode will not reach the breakdown value until a positive impulse is applied to its control anode by way of condenser N2. Since the positive impulse which fired tube CTRl is also applied to control anodes of all the odd numbered tubes but not to the control anodes of the even numbered ones, tube CTR2 cannot be fired on the same impulse which fired CTRI. In the. case of tube SI, the

potential applied to its control anode is insufii-- cient to fire said gap in the absence of large positive potential at the plate of tube SEL.

Soon after the beginning or the second half cycle of the signal train, which second half cycle is negative, the potential on the grid of the upper triode oi tube D1371! becomes sumciently negative to cut of! the fiow oi anode-cathode current. The resulting positive potential on the anode'is applied, through resistor R" and the lower triode of tube RE, used as a diode, to condenser A. As previously explained, this condenser is likewise kept in a charged state during most 0! the period of the reception of a positive halt cycle by the anode potential on the anode of the upper triode of tube INV, said potential being applied through resistor R50 and the lower diode of tube RE. In other words, during the reception of a train of positive and negative half cycles, condenser A is continually charged. Now resistor RII, which is virtually short-circuited during the charging of condenser A, appears in the discharge circuit of this condenser, which discharge circuit terminates at the potential available at the common terminal of resistors R48, R50 and R41. The ohmic resistance of resistor RSI and the capacity of condenser A are so computed that the time constant on discharge is long enough to prevent appreciable discharge of the condenser during the short instants between the latter part of each half cycle and the early part, of the following half cycle and, therefore, the potential on the grid of the upper triode oi said tube RE (via resistor R5!) is prevented from becoming negative.

Near the end of the second half cycle, the grid 01 the upper triode of tube DET: becomes positive with respect to the cathode. The anode potential now becomes more negative, applying a negative impulse through condenser C, to the grid of the lower triode of this tube. The resulting positive impulse on the anode'of this lower triode is applied, through condenser CN2, 0N4, CNS, CNI and CNO to the control anodes of the even numbered tubes CTR2, CTR, CTR, CTR8 and CTRI. Unaided, the magnitude of this impulse is insuificient to fire the control gaps of these tubes. Since, however, the current in the cathode circuit or tube CTRI has caused a positive bias to be applied to the control anode of tube CTR2 as previously explained, the latter tube is fired by the impulse. The resulting flow of current in the main gap of tube CTR! causes the cathode potential to become more positive and the anode potential more negative. bias to be applied to the control anodes of tubes CTR3 and S2, and the latter causes a neutralization of the positive bias applied to the control anode of tube SI by the flow of current in the cathode resistor of tube C'IRl. In this way, the tubes CTR- of the counting chain are fired in succession, each in turn biasing the control anode of the corresponding marking tube and the succeeding counting'tube, and neutralizing the bias of the preceding marking tube. It will now be shown that, in response to operations following the reception of a last pulse or half cycle in a signal train, the marking tube corresponding to the last fired counting tube will also be fired and remain in the conducting state, thus indicatin by its numerical designation the number of half cycles received. This tube remains in a fired condition until the last half cycle of a succeeding signal train is received, at which time the marking tube previously fired is extinguished and the marking tube indicative of the past pulse in the second signal train is fired. Obviously, if both signal trains contain the same number or half The former causes a positive 17 cycles, the same marking tube will remain lighted.

Suppose. for example, that signal is being received and that a previous signal train of three halt cycles ("3"), having been received, will have caused marking tube 83 to have become fired and to have remained lighted in the manner shortly to be explained. After the end of the filth halt cycle, no further signals will be received. Condenser A will then discharge through resistor RSI to the point where the grid of the upper triode oi the recycling tube RE becomes negative with respect to its cathode. The flow of anode current in this triode will thus be interrupted and the anode potential will become more positive,

carrying with it the grid of the lower triode of tube, INV. The anode potential of this latter triode becomes more negative applying a negative impulse through condenser D, to the grid of tube SEL. The resulting positive plate potential of tube SEL causes a positive impulse to be applied through conductor 6 and condensers SNI SNO to the control anodes of marking tubes SI S0, firing tube S5 since it is the only one of the marking tubes which is primed at this time.

In connection with tube S3, assumed to be previously conducting, the potential of its cathode is maintained at a constant positive value by the charge in condenser CC3 accumulated thereon by the voltage drop across the cathode resistor. It will also be noted that the anode current for any of the marking tubes is drawn through the resistor RBI, and the drop across this resistor, with one marking tube conducting, will still provide suilicient anode potential sothat the difierence between said anode potential and the potential maintained at the cathode of a conducting marking tube, like tube S3 by its associated charged condenser CO3, will be suflicient to keep the tube in a conducting condition. Now when tube S5 is fired subsequent to the reception of the fifth (and last) half cycle of the second signal train, the current through resistor RBI is increased since current now flows through both tubes S3 and S5. As a consequence, the voltage across resistor R8! is also increased and the voltage. available at the anode of the marking tubes is reduced a corresponding amount. Since condenser C03 is charged to a positive potential and condenser CC5 is uncharged at the time tube S5 is fired, the potential difference between the cathode and anode of tube S3 is now reduced below the sustaining value, in consequence of which tube S3 is extinguished. Onthe other hand, the potential difference between the anode and the cathode of tube S5 is the full difierence between the potential on the anode and that of the potential divider connected between the negative battery V and ground, and is sufficient to maintain the tube 55 in a conducting state.

It is now evident that if the second signal train contains the same number of half cycles as the first signal train, said first train already having caused the lighting of the appropriate marking tube, this tube remains lighted continuously. Thus, if tube S5 is lighted, the sustaining voltage is undisturbed between the successive signals. Although the control anode of tube S5 will be primed in the regular course of operations as already described, such priming will, of course, have no effect upon the tube since it is already conducting.

The more negative potential on the anode of the lower triode of tube INV is applied to the grid of tube EXT by way of resistors R54 and R53, from whose junction point a condenser E is bridged to ground. Said condenser delays the change of potential at thesrid of tube EXT sunlciently long to permit the above-described action of tube SEL to take place. Thereafter, the negative potential on the grid 01 the tube EXT causes the cathode thereof to become more negative. The potential applied thereby to the anodes of the counting tubes CTRI CTRU is now no longer sufllcient to sustain a discharge. Hence, counting tubes CTRI CTR5 extinguish. The marking tube S5, however, remains lighted. Otherwise the circuit is returned to its initial condition, ready for the receipt of the next signal train.

While we have described our invention in connection with its application to a specific signal transmitting and receiving arrangement, it is understood that various other applications and embodiments thereof may be made by those skilled in the art without departing from the spirit of the invention as defined by the scope of the appended claims. Thus, arelay may be included in the anode circuit of each of the marking tubes, which will operate when the tube is rendered conducting, in turn operating a suitable register circuit that includes steering devices for switching the relays from one register to the next; thus registering a series of numbers indicative of the number of half cycles in each of the signal trains received.

It is also apparent that, by doubling the number of counting tubes and marking only every other pulse, the signal transmitted can be represented by the number of whole cycles instead of half cycles.

What is claimed is:

1. The combination with an electronic counting chain comprising a number of gas-filled tubes and an electronic marking chain comprising an equal number of gas-filled tubes, of means responsive to a signal for operating one of the tubes in said counting chain and priming the corresponding tube in said marking chain, said means being responsive tothe next signal for operating the next tube in said counting chain, priming the corresponding tube in said marking chain and disabling the preceding tube in said marking chain.

2. The combination with an electronic counting chain comprising a number of gas-filled tubes and an electronic marking chain comprising an equal number of gas-filled tubes, of means responsive to a signal for operating one of the tubes in said counting chain and priming the corresponding tube in said marking chain, said means being responsive to the next signal for operating the next tube in said counting chain, priming the corresponding tube in said marking chain and disabling the preceding tube in said marking chain, and means responsive subsequent to the reception of the last signal for operating said primed tube in said marking chain and extinguishing the operated tubes in said counting chain.

3. In a receiver for alternating current impulses, the combination with an electronic counting chain comprising a number of gas-filled tubes and an electronic marking chain comprising an equal number of gas-filled tubes, of means responsive to a train of alternating current impulses for operating the tubes of said counting chain in succession and for priming the corresponding tubes of said marking chain in succession, means responsive to the operation of a tube in said counting chain for disabling the preceding tube in said marking chain, a condenser, means assmsi- 19 responsive to said train of impulses mcharging and maintaining charged said condenser during the reception of successive impulses, and means responsive to the discharge of said condenser subsequent to the reception oi the last impulse in the train for operating theprimed' tube in said marking chain and extinguishing said operated tubes in said counting chain whereby said operated tube in said marking chain indicates the number of impulses in the train.

4. In an alternating current signaling system the combination with a transmission line, of a receiver connected to said line adapted for response to the positive and negative halt cycles. respectively, of a continuous alternating current substantially sinusoidal in character transmitted over said line, comprising a two-stage direct current amplifier, a first detecting, inverting and amplifying means responsive to positive halt cycles, a second detecting and amplifying means responsive to negative halt cycles, a first plurality of gas-filled tubes arranged as a counting chain, said tubes being rendered conducting in succession by impulses produced by said first and second amplifying means in consequence of the termination of each positive and negative half cycles to which said first and second ampIifying means respectively respond, a second plurality of gasa 20 iilled tubes arranged as a marking chain, means REFERENCES CITED The following references are oi record in the file of this patent:

UNITED s'ra'ms PA'I'EN'I'S Number Name Date 2,272,070 Reeves Feb. 3, 1942 2,308,778 Prince Jan. 19, 1943 2,373,134 Massonneau Apr. 10, 1945 2,401,657 Mumma June 4, 1946 2,422,583 Mumma June 1'7, 194'! FOREIGN PATENTS Number Country Date 567,863 Great Britain Mar. 6,1945 

